Users had been asking for a storage version of VMware's VMotion tool, which moves running virtual machines (VMs) from one physical server to another. With Storage VMotion, VMware adds the ability to migrate running virtual machine disk files within and across data storage systems with no downtime, ensuring continuous service availability and transaction integrity.

Storage VMotion "set the standard for virtual guest availability," according to one judge. "It increases application uptime and IO flexibility -- the reason most [people] buy VMware today."

Storage VMotion works by moving a virtual machine's home directory (containing information on configuration, log files, etc.) to the new location before moving the virtual machine disk file. It creates a "child disk" for each virtual machine being migrated, and all disk writes are directed to that child disk once the migration starts. The parent, or original virtual disk, is then copied from the old storage device to the new one. The child disk is reunited and consolidated with the new parent disk, and the ESX host server is redirected to the new parent disk location.

The product is most useful for VMware customers who want to minimize service disruption while performing maintenance or migrating to new storage systems or different classes of storage. It's also helpful for balancing or optimizing storage workloads and addressing performance bottlenecks. Storage VMotion supports both FC and iSCSI SANs, and works with any operating system and application that runs on the VMware Infrastructure.

Customers who buy the Enterprise Edition of VMware Infrastructure 3 -- the server virtualization platform that includes VMware ESX Server 3.5 -- get Storage VMotion as part of the package. List price is $5,750 per two processors. Both VMotion and Storage VMotion require VMware vCenter Server (licensed separately) to enable central management of the entire VMware virtual environment from a single console.

VMotion and Storage VMotion are available as part of a standalone package for purchasers of the less expensive Foundation and Standard versions of VMware Infrastructure. The standalone price is $3,495 per dual processor.